1. Field of the Invention
The present invention relates to a thermistor composition having a preferred resistance value and B constant and being available in a wide temperature range from room temperature to higher temperatures such as 400.degree. C.
2. Description of the Related Art
Sintered products, such as metal oxides of the Mn--Ni or Mn--Ni--Co composition, have been known as thermistors in the art.
These thermistor compositions are desired to have a wide range of resistivity. Various types of thermistor composition have been provided in response to this requirement. The sintered substance has a B constant of approximately 2,000-5,000 K and its resistance value varies by 2-5% when the temperature varies by 1.degree. C. near room temperature. Therefore, it is possible to measure the temperature at a high precision, approximately 1/100+L .degree. C. on the basis of the resistance value of such a thermistor. Accordingly, it can be widely used as a temperature sensor near room temperature due to this property.
The thermistor used near room temperature, however, is disadvantageous because its resistivity varies remarkably when it is used at temperatures above 250.degree. C. for a long period of time.
In order to solve this problem, JP 62-11201A discloses a thermistor device having a metal oxide of the Mn--Ni composition into which SiO.sub.2 is added, wherein the variation of resistance characteristic in a high temperature range of 300-500.degree. C. is reduced. This thermistor device, however, is not suitably available near room temperature because its resistivity increases remarkably.